Recovery of uranium by electrolysis of a fused bath



RECOVERY OF URANIUM BY ELECTROLYSIS OF A FUSED BATH George Meister, Newark, N. J., assignor to the United States of America as represented by the United States Atomic Energy Commission No Drawing. Application January 31, 1944, Serial No. 520,550

3 Claims. .(cr. 204-64) This invention relates to a method for the recovery of uranium and more particularly tofused electrolytes and their method of use in the recovery of uranium in coalescent form by electrodeposition.

Methods and apparatus for the recovery of uranium by electrolysis are described in the copending application Serial No. 478,270, filed March 6, 1943, by Lilliendahl et al., now U. S. Letters Patent No. 2,690,421 issued September 28, 1954. The present invention relates to improvements in the methods disclosed therein for the electrolysis of potassium uranous fluoride, KUF5, known as green salt, and relates especially to an improved composition of fused salt electrolytes, and to improved methods of recovering uranium from various uranium halides and uranium oxyhalides introduced into such electrolytes. It has been found that uranium may be recovered efiiciently by electrodeposition from a fused salt electrolyte at temperatures above the melting point of uranium, and that a sodium-free, barium halide type of electrolyte has definite advantages.

It is the principal object of this invention to provide an improved fused salt electrolyte for the recovery of uranium in coalescent form by electrodeposition.

It is a further object of this invention to provide a method for electrodepositing uranium substantially free from undesirable impurities.

It is another object of this invention to provide a fused salt electrolyte composition free of alkali metals and alkali compounds for the recovery of uranium free from alkali impurities.

It is another object of this invention to provide a fused salt electrolyte composition suitable for the electrolysis of uranium therefrom at temperatures above the melting point of uranium.

It is still another object of this invention to provide a fused salt electrolyte composition suitable for the electrolysis of uranium halides and uranium oxyhalides at temperatures above the melting point of uranium.

Other objects and advantages of the invention will be readily apparent to those skilled in the art from the following description of preferred methods and compositions embodying my invention.

The present method may be successfully practiced by the use of an electrolyte bath including a component having a melting point above the melting point of uranium, such as barium fluoride, BaFz, with a melting point of about 1280 C. A bath containing a substantial proportion of barium fluoride and barium chloride, BaClz, gives excellent results, and enables the recovery of sodium-free uranium from uranium halides and from uranium oxyhalides.

The electrolysis of uranium halides, such as uranium tetrafluoride, UF4, potassium uranium fluorides, KUFs (green salt) and KaUFs, is accomplished by adding one or more of the halides to a fused salt electrolyte bath held within a suitable crucible, and electrolyzing the mixture to cause uranium metal to be deposited at the cathode. A fused salt electrolyte including barium fluotes Patent 2,774,729 ,..Patente d Dec. 18, 1956 The salt bath may be fused, in accordance with the disclosure of said copending application, by heating the crucible. After the electrolysis process is started, the bath may be maintained in the fused condition by the electrolysis current alone- Upon the addition of a uranium halide to the bath, it is believed that complex salts of the UFr-BaFz type are formed. The electrolysis proceeds with the electrodeposition of uranium at the cathode.

The melting point of uranium appears to be about ll29i4 C., and the melting point of the complex salt containing electrolyte is about 1150 C. When using the bath composition described herein, the fused bath temperature is thus above the melting point of uranium, and the molten uranium collects at the cathode in coalescent form. The molten uranium metal may be tapped from the bottom of the crucible, or may be allowed to solidify before being removed.

A uranium oxyhalide may be introduced into the fused salt bath in place of a uranium halide. A uranium oxysalt, such as UO2F2, added to the bath composition mentioned, is believed to form a complex salt, UOzFz'BaFz. Other complex salts which may be used include UOzFz-ZBaFz, UO2Fz-3BaFz and mixtures such as xBaFz-yUOz-zUF r. When uranium oxyhalides are used, the fused bath temperature should be maintained about 50 C. or more above the melting point of the complex salts, that is, at about 1250 C., in order to obtain good electrodeposition of the uranium.

As previously noted, the electrolysis of uranium compounds in the fused salt bath is accomplished at tempera tures above the melting point of uranium, and the bath temperature should be above 1150 C. when electrolyzing uranium halides, and should be above 1250 C. when electrolyzing uranium oxyhalides. The use of barium halides for the bath composition in place of alkali metal halides, such as sodium chloride, avoids the presence of alkali metal compounds in the bath, and hence provides an electrodeposit of uranium substantially free of alkali metal impurities which latter are diflicult to remove and impair the purity of the uranium metal product. The electrolysis of uranium compounds in the fused bath disclosed herein may be made a continuous process by introducing additional uranium compounds from time to time, as well as adding enough barium fluoride or other alkali-free salt to maintain the necessary proportions in the fused bath for electrolysis at temperatures above the melting point of uranium.

The recovery of uranium by electrodeposition at temperatures above 1129" C.i4 C. is found to be exceedingly efficient, and the coalescent form of the deposit provides a pure metal not requiring expensive crushing, washing, grinding, sintering and fusing operations to make it a suitable commercial product. The coalescent molten uranium may be cast into desired shape by pro viding the crucible with a bottom tap.

Various changes and substitutions may be made in the methods and compositions described herein without departing from the spirit and scope of my invention as defined in the following claims.

I claim:

1. The method of recovering metallic uranium from uranium halides which comprises the steps of providing a fused electrolyte consisting essentially of barium fluoly'iing'" said mixture at approximately 1150 C. to electro deposit uranium therefrom in coalescent form.

3;- The method of recovering metallic uranium from uranium halides which comprises the' steps of providing a; fused electrolyte consisting essentially of 90% barium fluoride and 10% bariumchloride by weight, adding potassium uranou's fluoridetosaid electrolyte, and electrolyzi'ng' said mixture at a temperature of approximately 11 50, C. to e'lect'rodep'osit uranium therefrom in coales- Cent fdrin.

References Cited in the file of this patent UNITED STATES PATENTS 1,511,829 Dickinson Oct. 14, 1924 1,673,043 Fischer June 12, 1928 1,821,176 Driggs et al. Sept. 1, 1931 1,833,425 Iessup Nov. 24, 1931 1,861,625 Driggs et a1; June 7, 1932 1,874,090 Drigg's Aug. 30, 1932 2,049,291 Qomstock July 28, 1936 2,261,905 Nelson et al Nov. 4; 1941' OTHER REFERENCES International Critical Tables, ol. IV, page 65; 1928.

Industrial and Engineering Chemistry, vol. 22, pages 516-519; May 1930.

Handbook of Chemistry and Physics, 27th edition, by Hodgman, pages 482 and 483.

Stock: Article in" Transactions of the Electrochemical 

1. THE METHOD OF RECOVERING METALLIC URANIUM FROM URANIUM HALIDES WHICH COMPRISES THE STEPS OF PROVIDING A FUSED ELECTROLYTE CONSISTING ESSENTIALLY OF BARIUM FLUORIDE AND BARIUM CHLORIDE, ADDING A URANIUM FLUORIDE TO SAID FUSED ELECTROLYTE AND ELECTROLYZING SAID MIXTURE AT A TEMPERATURE OF APPROXIMATELY 1150* C. TO ELECTRODEPOSIT URANIUM THEREFROM IN COALESCENT FORM. 